1. Field of the Invention
Apparatuses and methods consistent with the disclosure provided herein relate to diagnosing diseases such as glaucoma which damage optic nerve, and more particularly, to an apparatus and a method for diagnosing diseases associated with optic nerve by measuring a thickness of retinal nerve fiber layer (RNFL) using methods including optical coherence tomography (OCT) or scanning laser polarimetry (SLP).
2. Description of the Related Art
Among many eye diseases that affect optic nerve, glaucoma is a group of eye diseases that damages the optic nerve and impairs the vision field in a characteristic pattern due to risk factors such as elevated intraocular pressure. Glaucoma leaves permanent loss of visual field to a patient unless diagnosed and treated properly at the early stage. Therefore, it is very important to detect several variants associated with glaucoma and attend to them early on. It is important to do so especially for the case of glaucoma, since glaucoma sometimes does not develop the elevated intraocular pressure (that is, intraocular pressure sometimes remains in normal range) or other eye problems and so is left undiagnosed and untreated.
There are many tests including ophthalmoscopy, stereography or perimetry conducted to detect glaucoma in the early stage. However, the drawback of inspecting optic nerve by the ophthalmoscopy and stereography is that it is difficult to detect the minute changes in the early stage and the evaluation is subjective. The perimetry is relatively more objective inspection than the above-mentioned tests, but considering the study results which indicate that the perimetry is not able to detect the abnormality until approximately 40% of damages are done to the retinal ganglion cells, the perimetry has a limit as a method to diagnose early-stage of glaucoma.
Accordingly, many tests have been suggested for early diagnosis of glaucoma, and these tests focus more on the glaucomatous changes which occur before the abnormality becomes detectable by the perimetry.
Among various changes associated with glaucoma, it has been reported that the change in the retinal nerve fiber layer (RNFL) precedes the change in the optic disk and vision field. Accordingly, it has been suggested that it would be efficient to inspect the RNFL for the early diagnosis of glaucoma.
Various equipments have been developed to be used to detect the changes in the RNFL. Among these, the optical coherence tomography (OCT) and the scanning laser polarimetry quantitate the thickness of the RNFL based on the reflection from a border between retina and vitreous to measure the thickness of four peripapillary sectors in upper, lower, nose and ear directions, the thickness of the twelve clock-hour sectors, and the average of all the obtained thickness. Many studies suggest that the OCT and the scanning laser polarimetry are useful methods to diagnose glaucoma in the early stage, since the OCT images help to detect a change of the RNFL which becomes thinner at a location where the visual field defect develops.
Generally, glaucoma is diagnosed using OCT and scanning laser polarimetry based on a comparison between the thickness of the RNFL as measured and the thickness of a normal healthy subject. However, considering the fact that even healthy RNFLs without glaucoma vary in the thickness depending on persons, and the average thickness of the healthy RNFL varies depending on areas, the sensitivity and specificity have yet to be improved particularly in relation to early diagnosis of glaucoma.